sound
DESCRIPTION
sound very good chapterTRANSCRIPT
Longitudinal wave
requires a medium
(cannot travel in a vacuum)
Is known as
ACOUSTICS
A sound is a vibration
The vibrating causes the air molecules near the movement to be forced closer. This is called compression
As the vibration moves on, the density and air pressure becomes lower than normal and is called rarefaction
Pressure wave – longitudinal
Frequency = pitch
v = 334 m/s in air at room temperature
Velocity is dependent upon the material
Do molecules move faster or Do molecules move faster or slower as temperature slower as temperature
increases?increases?So would sound travel faster So would sound travel faster
or slower as temperature or slower as temperature increases?increases?
Waves travel fastest in solids, slowest in gases.
SolidSolid LiquidLiquidGasGas
•Fastest in solids, slowest in gases.
Air = 340 m/swater= 1440 m/ssteel = 5000 m/s•Supersonic: faster than the speed of sound.
Sound travels faster in warm water than in cold water
By measuring the time it takes for sound to travel a known distance through the ocean the average temperature of the water can be calculated = ATOC (acoustic thermometry of ocean climate)
Air Air
HeliumHelium
HydrogenHydrogen
WaterWater
Sea waterSea water
Iron/SteelIron/Steel
GlassGlass
AluminumAluminum
343 m/s
1005 m/s
1300 m/s
1440 m/s
1560 m/s
≈5000 m/s
≈ 4500 m/s
≈ 5100 m/s
The highness or lowness of sound. Depends on the frequency of sound waves.
High frequency = High pitch Low frequency = Low pitch
•Also called LOUDNESS•Amount of energy•Depends on the amplitude of sound waves. (amplifier)
Large Amp. = Loud sound Small Amp. = Soft sound
Unit is the “Bell”. Named after Alexander Graham Bell
More commonly used is the decibel (dB)
= 0.1 Bell
(in dB) = 10 log(I/I0)
I is the intensity ( A2)
I0 = 1.0 x 10 -10 W/m2 the “threshold of hearing”
Jet plane at 30 m
Threshold of pain
Indoor rock concert
Auto interior
Street traffic
Conversation
Whisper
Rustle of leaves
140
120
120
75
70
65
1x10-10
1x10-11
•Sound waves reflecting from hard surfaces•Ex.: Multiple echo resulting from the direct sound and the reflected sound
Near total silence - 0 dB
A whisper - 15 dB
Normal conversation - 60 dB
Lawnmower - 90 dB
Threshold of pain - 120 dB
A rock concert or a jet engine - 120 dB
Gunshot, firecracker - 140 dB
Near total silence - 0 dB
A whisper - 15 dB
Normal conversation - 60 dB
Lawnmower - 90 dB
Threshold of pain - 120 dB
A rock concert or a jet engine - 120 dB
Gunshot, firecracker - 140 dB
Measurement of loudness
Measurement of loudness
Infrasonic: Infrasonic: below 20 Hz (below our hearing)
Ultrasonic Sound: Ultrasonic Sound: above 20,000Hz (above our hearing)
Ultrasound can be used to create internal images of the human bodyEx. Pregnant woman gets a “picture” of
her unborn baby
An equal mixture of all An equal mixture of all frequencies of soundfrequencies of sound
Used to calm stressUsed to calm stress
Used in office buildingsUsed in office buildings
Yep! There is such a thingYep! There is such a thing
Causes:Causes:
Damage to ear resulting in hearing Damage to ear resulting in hearing lossloss
StressStress
Caused by destructive interference
Result – hardly any or no sound
Bad for concert halls – designers be careful!
Used to locate underwater objects
and distances.
***Reflection**
Apparent change in frequency (pitch) Apparent change in frequency (pitch) of a sound from a moving source.of a sound from a moving source.
Source moving toward observer:Source moving toward observer:f’ = f / (1-vf’ = f / (1-vss/v)/v)
Source moving away from observer:Source moving away from observer:f’ = f / (1+vf’ = f / (1+vss/v)/v)
f = frequency of source, f = frequency of source,
f’=frequency heard by observer, f’=frequency heard by observer,
vvss = velocity of source, v = velocity of = velocity of source, v = velocity of soundsound
Change in pitch due Change in pitch due to motion.to motion.
*Moving toward *Moving toward increasesincreases the the pitchpitch
*Moving away decreases the *Moving away decreases the pitchpitch
*Think of sirens*Think of sirens
Amazing Water & Sound Experiment #2[hd720].mp4